This invention relates to a catalyst for use in auto emission control which has improved hydrothermal stability as well as improved poison resistance and especially for an improved three-way catalyst (TWC).
As we described in our copending application U.S. Ser. No. 461,119, filed Jan. 26, 1983,now U.S. Pat. No. 4,476,246, performance of alumina-supported Pt-Rh or Pt-Pd-Rh TWC could be substantially improved by doubly promoting the catalyst with ceria and the oxides of alkali metals, especially of Li. The improvement in TWC performance is manifested in both high conversion efficiency as well as in good durability which is far superior to the singly promoted TWCs with ceria. Upon repeated exposures to severely hydrothermal conditions, however, sintering takes place along with interaction of the catalytic materials either among themselves or with exhaust contaminants. In addition, the support undergoes a phase transition to the undesired alpha-alumina form and as a cumulative result there is a decrease in TWC performance.